Driving method for liquid crystal display panel

ABSTRACT

A driving method for a liquid crystal display (LCD) panel for displaying a frame having a first field and a second field on the LCD panel is provided. The driving method includes transmitting horizontal scan lines of the frame to the LCD panel using a line pair method and displaying the frame on the LCD panel using a column inversion method. Therefore, the driving method of the present invention can increase the resolution of the displayed frame without the need to provide additional memories or deploying complex algorithms.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 94117617, filed on May 30, 2005. All disclosure of the Taiwanapplication is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving method for a liquid crystaldisplay (LCD) panel. More particularly, the present invention relates toa driving method for an LCD panel for displaying a television (TV)signal.

2. Description of the Related Art

A TV signal is generally displayed in an interlacing method such thateach frame of the TV signal has an odd field and an even field. In theTV signal, the scan lines of a field (e.g. an odd field) are interlacedbetween the scan lines of another field (e.g. an even field).

FIG. 1 is a diagram showing an interlacing TV signal. As shown in FIG.1, using NTSC TV system as an example, a frame has altogether 525 scanlines. Nevertheless, after deducting the scan lines for flyback, thenumber of the remaining scan lines which are effective is 484. Theeffective scan lines are labeled 1, 2, 3, . . . , 482, 483 and 484respectively. Further, a frame is built by an odd field and an evenfield. The odd field includes the scan lines labeled 1, 3, 5, . . . ,481 and 483 while the even field includes the scan lines labeled 2, 4,6, . . . , 482 and 484. Furthermore, other TV systems such as PAL aresimilar to NTSC.

FIG. 2 is a diagram showing the TV signal displayed through an LCD. Inpractice, the driving method for the display panel of the LCD includesenabling each scan line of the LCD panel and transmitting correspondingdata through data lines of the LCD panel when a particular scan line isactivated. The corresponding data can be the data contained in oneeffective scan line of either the odd field or the even field.Therefore, the data in one of the effective scan lines (non-physical) ofeither the odd field or the even field is called ‘horizontal scan line’,which is to distinguish it from one of the scan lines (physical) of theLCD panel.

As shown in FIG. 2, the letters X and Y represent the label sets of thedata lines and the scan lines of the LCD panel respectively. The letterT represents the label set of the horizontal scan lines of the TVsignal. When an LCD panel having 240 scan lines is used to display aframe having 484 horizontal scan lines (that is, each of the odd and theeven field has 242 horizontal scan lines), the odd and the even field ofeach frame are displayed in an interlacing method. For example, on theLCD panel, the odd field of a first frame is displayed and then followedby displaying the even field of the first frame. Then, the odd field ofa second frame is displayed and then followed by displaying the evenfield of the second frame. In this way, the odd field and the even fieldof each frame are displayed alternately.

Obviously, displaying the 242 horizontal scan lines of an odd field (oran even field) on the LCD panel having 240 scan lines cannot escapelosing two horizontal scan lines. In general, the first and the lasthorizontal scan lines are discarded or some other scheme is used withoutmuch effect on the entire frame. To prevent the unidirectionalapplication of an electric field on the liquid crystals that may lead toa deterioration of the twisting property of the liquid crystal, theliquid crystals are alternately driven through a polarity inversiondriving method. For example, FIG. 2 shows the column inversion which isone of the polarity inversion driving methods. Other types of thepolarity inversion driving methods include row inversion, frameinversion and dot inversion.

In the conventional technique, if an LCD panel having 240 scan lines isused to display an TV signal comprising an odd field and an even fieldeach having 242 horizontal scan lines, the maximum resolution of thedisplayed frame is only 240 scan lines. To increase the resolution, thenumber of scan lines of the LCD panel must be increased, for example, to480 scan lines. Thus, there is a need to provide additional memories tostore the previous field (having 242 horizontal scan lines) so that itcan match with the next field (having 242 horizontal scan lines) so todisplay together on the LCD panel (having 480 scan lines).Alternatively, some memories together with sophisticated algorithms canbe used to provide the resolution higher than the 480 scan lines of theLCD panel (having 480 scan lines).

SUMMARY OF THE INVENTION

Accordingly, at least one objective of the present invention is toprovide a driving method for an LCD panel so that the resolution ofdisplayed frames is increased without the need for providing additionalmemories or using sophisticated algorithms.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, theinvention provides a driving method for an LCD panel for displaying aframe on the LCD panel. The LCD panel has M scan lines and N data lines.The frame includes a first field and a second field. Each of the firstand the second field includes L horizontal scan lines. The drivingmethod includes sequentially receiving and transmitting the horizontalscan lines of the first field to the LCD panel to display the firstfield on the LCD panel; and sequentially receiving and transmitting thehorizontal scan lines of the second field to the LCD panel to displaythe second field on the LCD panel thereafter.

When the first field is displayed on the LCD panel, P of the horizontalscan lines of the first field are transmitted to two consecutive scanlines of the LCD panel respectively, and Q of the horizontal scan linesare transmitted to one scan line of the LCD panel respectively.Furthermore, the order of any two of the horizontal scan linestransmitted to the LCD panel is identical to the order of any two ofhorizontal scan lines of the first field. Meanwhile, the signal polarityof odd-numbered data lines of the data lines and the signal polarity ofeven-numbered data lines of the data lines of the LCD panel are a firstpolarity and a second polarity respectively.

When the second field is displayed on the LCD panel, R of the horizontalscan lines of the second field are transmitted to two consecutive scanlines of the LCD panel respectively, and S of the horizontal scan linesare transmitted to one scan line of the LCD panel respectively.Furthermore, the order of any two of the horizontal scan linestransmitted to the LCD panel is identical to the order of any two of thehorizontal scan lines of the second field. Meanwhile, the signalpolarity of the odd-numbered data lines of the data lines and the signalpolarity of the even-numbered data lines of the data lines of the LCDpanel are the second polarity and the first polarity respectively.

Wherein, L, M, N, P and R are natural numbers, Q and S are non-negativeintegers, P+Q≦L and R+S≦L. In addition, the first polarity and thesecond polarity represent the voltage level of the input signal at oneof the data lines relative to the common electrode on the uppersubstrate. In the present embodiment, the first polarity and the secondpolarity are two reverse polarities. For example, if the first polarityhas a positive value, the second polarity has a negative value. Theodd-numbered data lines have positive values (the even-numbered datalines of the first field have negative values) when the first field isdisplayed and the odd-numbered data lines have negative values (theeven-numbered data lines of the second field have positive values) whenthe second field is displayed. In other words, the column inversion ofthe polarity inversion driving method is used.

It should be noted that in the prior technique shown in FIG. 1 thehorizontal scan lines of the odd field are labeled 1, 3, 5, . . . , 2n−1 and the horizontal scan lines of the even field are labeled 2, 4, 6,. . . , 2 n where n is a positive integer. However, to systematize theexplanation in the present invention, the horizontal scan lines of boththe odd field and the even field are labeled using 1, 2, 3, . . . , nand so on. Therefore, the first, the second, the third horizontal scanlines of the odd field are equivalent to the first, the third and thefifth horizontal scan lines respectively in FIG. 1. Similarly, thefirst, the second and the third horizontal scan lines of the even fieldare equivalent to the second, the fourth and the sixth horizontal scanlines respectively in FIG. 1 and so on.

In one embodiment, P+Q=R+S=L, where Q≠0 and S≠0. Therefore, a few of thehorizontal scan lines of the first field (and the second field) aretransmitted to two consecutive scan lines of the LCD panel respectivelywhile the remaining of the horizontal scan lines of the first field (orthe second field) are transmitted to one scan line of the LCD panelrespectively. In another embodiment, P+Q<L, R+S<L, Q≠0 and S≠0.Therefore, a few of the horizontal scan lines of the first field (or thesecond field) are transmitted to two consecutive scan lines of the LCDpanel respectively while some of the remaining of the horizontal scanlines are transmitted to one scan lines of the LCD panel respectively.In these two embodiments, when the first field is displayed, the h^(th)horizontal scan line of the first field is transmitted to the g^(th)scan line of the LCD panel. On the other hand, when the second field isdisplayed, either one of the (h−1)^(th), the h^(th) and the (h+1)^(th)horizontal scan lines is transmitted to the g^(th) scan line of the LCDpanel. Here, h and g are natural numbers such that h≦L and g≦M. Bothembodiments are applicable when the horizontal scan lines of the firstfield (or the second field) are driven by a line pair driving method andthe number of the horizontal scan lines is larger than the number of thescan lines of the LCD panel.

In brief, the driving method for the LCD panel according to the presentinvention utilizes the line pair driving method to transmit thehorizontal scan lines of the frame to the LCD panel and the columninversion driving method to display the frame on the LCD panel. Hence,the resolution of the frame can be increased without the need to provideadditional memories or use sophisticated algorithms.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a diagram showing an interlacing TV signal.

FIG. 2 is a diagram showing the interlacing TV signal displayed throughan LCD.

FIGS. 3A and 3B are diagrams showing driving methods for an LCD panelaccording to one preferred embodiment of the present invention.

FIG. 4 is a diagram showing a driving method for an LCD panel accordingto another preferred embodiment of the present invention.

FIG. 5 is a diagram showing a driving method for an LCD panel accordingto yet another preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

To explain the embodiment of the present invention more clearly, thefirst field and the second field in the following description are an oddfield and an even field and the first polarity and the second polarityare a positive value and a negative value respectively.

FIGS. 3A and 3B are diagrams showing driving methods for an LCD panelaccording to one preferred embodiment of the present invention. Themethod is particularly suitable when the horizontal scan lines of theodd field (or the even field) are driven by a line pair driving methodand the number of the horizontal scan lines is equal to the number ofthe scan lines of the LCD panel.

As shown in FIG. 3A, the rightmost diagram with the heading ‘Horizontalscan line (T) of TV signal’ and the middle diagram with the heading‘Horizontal scan line (Z) of TV signal’ are intrinsically the sameframe. The former horizontal scan lines are labeled using the labelingmethod in FIG. 1 and the latter horizontal scan lines are labeled usingthe labeling method according to the present invention. Similarly, asshown in FIG. 3B, the rightmost diagram with the heading ‘Horizontalscan line (T) of TV signal’ and the middle diagram with the heading‘Horizontal scan line (Z) of TV signal’ are intrinsically the sameframe. The TV signal are displayed in an interlacing method; forexample, the TV signal is specified by NTSC or PAL.

To facilitate the explanation, the letters Y, Z and T in the descriptionwill represent ‘Scan line (Y) of LCD panel’, ‘Horizontal scan line (Z)of TV signal’ and ‘Horizontal scan line (T) of TV signal’ respectively.

As shown in FIGS. 3A and 3B, the LCD receives the interlacing TV signalsimilar to that shown in FIG. 1. Each frame of the TV signal includes anodd field and an even field. Each of the odd field and the even fieldcomprises L horizontal scan lines (L is 242, for example). In FIG. 3A,only one representative frame (the Z or T) is shown. However, anyonefamiliar with the technique will notice that the driving method in thepresent invention aims at each frame of the interlacing TV signal.Because the present invention uses a line pair driving method to drivethe LCD, the display panel of the LCD at least requires M scan lines andN data lines. Here, M<2L. In the following description, M=480 and L=242are used as an example.

The so-called ‘line pair’ driving refers to the transmission of eachhorizontal scan line of the odd field or the even field to twoconsecutive scan lines of the LCD panel. Furthermore, the order of anytwo of the horizontal scan lines transmitted to the LCD panel isidentical to the order of any two of the horizontal scan lines of thefirst field. For example, one frame of the original TV signal includesthe horizontal scan lines {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, . . .}. Therefore, the odd field includes the horizontal scan lines {1, 3, 5,7, 9, 11, . . . } and the even field includes the horizontal scan lines{2, 4, 6, 8, 10, 12, . . . }. The horizontal scan lines {a, b, c}represent an ordering relation of the a^(th), the b^(th) and the c^(th)horizontal scan lines. The horizontal scan lines {1, 3, 5, 7, 9, 11, . .. } become {1, 1, 3, 3, 5, 5, . . . } after the horizontal scan linesare converted into line pairs. Similarly, the horizontal scan lines {2,4, 6, 8, 10, 12, . . . } become {2, 2, 4, 4, 6, 6, . . . } after thehorizontal scan lines are converted into line pairs.

However, in order to improve the resolution of the displayed frame, thescan lines at both sides should be staggered, such as ‘T’ shown in FIG.3A. The horizontal scan lines of the odd field become {1, 3, 3, 5, 5, 7,. . . } while the horizontal scan lines of the even field remainunchanged as {2, 2, 4, 4, 6, 6, . . . }. Thus, the first horizontal scanline do not use line pair method. Alternatively, as ‘T’ shown in FIG.3B, the horizontal scan lines of the odd field are to be kept unchangedas {1, 1, 3, 3, 5, 5, . . . } while the horizontal scan lines of theeven field become {2, 4, 4, 6, 6, 8, . . . }.

The driving method of the present invention can be explained in anotherway using the Z in FIG. 3A. When a frame (including the odd field andthe even field of Z) of a TV signal is displayed, first the odd field ofZ is displayed on the first frame of the LCD panel. Then, the even fieldof Z is displayed on the second frame of the LCD panel. The first andthe second frames are actually the displayed frame on the same displaypanel but at a different time. Hence, the first and the second frameshave the same scan line label.

When the odd field of Z is displayed on the LCD panel (or the firstframe), the first horizontal scan line of the odd field of Z istransmitted to the first scan line of the LCD panel (or the first frame)and the j^(th) horizontal scan line of the odd field of Z is transmittedto the (2j−2)^(th) and the (2j−1)^(th) scan lines (here, j=2, 3, . . . ,239; in other words, j is a natural number and 1<j≦L) of the LCD panel(or the first frame), and the 241^(st) horizontal scan line of the oddfield of Z is transmitted to the 480^(th) (M^(th)) scan line of the LCDpanel (or the first frame). When the even field of Z is displayed on theLCD panel (or the second frame), the i^(th) horizontal scan line of theeven field of Z is transmitted to the (2i−1)^(th) and the 2i^(th) scanlines (here, i=1, 2, 3, . . . , 240; in other words, i is a naturalnumber and i<L) of the LCD panel (or the second frame).

In FIGS. 3A and 3B, the diagram on the left with the heading Y lists outthe scan line labels of the LCD panel but without the data line labels.However, the driving method of the present invention still needs tomatch up with the polarity inversion driving method described in FIG. 2to prevent any deterioration of the liquid crystal twisting property.The present invention uses a line pair driving method. Furthermore, thepolarity inversion of the LCD panel uses a column inversion drivingmethod.

FIG. 4 is a diagram showing a driving method for an LCD panel accordingto another preferred embodiment of the present invention. The presentmethod is particularly suitable when the horizontal scan lines of theodd field (or the even field) are driven in line pairs and the number ofhorizontal scan lines is greater than the number of scan lines of theLCD panel. For example, if each of the odd field and the even field hasL horizontal scan lines (for example, 286 horizontal scan lines), theneach has 2L horizontal scan lines (for example, 572 horizontal scanlines) after the line pair driving. However, the LCD panel has only Mscan lines (for example, 468 scan lines).

As shown in FIG. 4, the driving method of the present invention includestransmitting P of the horizontal scan lines of the odd field and theeven field to two consecutive scan lines of the LCD panel respectively.The remaining Q horizontal scan lines are transmitted to one scan lineof the LCD panel respectively. Here, P+Q=L, and P, Q, L are naturalnumbers. Then, the odd field and the even field are displayed on the LCDpanel. It should be noted that the labels bracketed by dotted linesrepresent the horizontal scan lines with respect to the labels do notuse line pairs and (*1) represents the condition that there is one lessline after using the line pair method.

For example, the odd field of Z in FIG. 4 includes the horizontal scanlines {1, 2, 2, 3, 4, 4, 5, 5, 6, 7, 7, 8, 8, 9, 10, 10, . . . }. Itshows that the horizontal scan lines {2, 4, 5, 7, 8, 10, 11, 13, . . . }of the horizontal scan lines {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, . .. } included in one frame of the original TV signal are transmitted totwo consecutive scan lines of the LCD panel respectively. The remaininghorizontal scan lines {1, 3, 6, 9, 12, . . . } are transmitted to onescan line of the LCD panel respectively. Similarly, the even field of Zin FIG. 4 includes the horizontal scan lines {1, 1, 2, 2, 3, 4, 4, 5, 5,6, 7, 7, 8, 8, 9, . . . }. It shows that the horizontal scan lines {1,2, 4, 5, 7, 8, 10, 11, 13, . . . } of the horizontal scan lines {1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, . . . } included in one frame of theoriginal TV signal are transmitted to two consecutive scan lines of theLCD panel respectively. The remaining horizontal scan line {3, 6, 9, 12,. . . } are transmitted to one scan line of the LCD panel respectively.

FIG. 5 is a diagram showing a driving method for an LCD panel accordingto yet another preferred embodiment of the present invention. Thecondition of applicability is similar to the one in FIG. 4. As shown inFIG. 5, the driving method of the present invention includestransmitting P of the horizontal scan lines of the odd field and theeven field to two consecutive scan lines of the LCD panel respectively.The remaining Q horizontal scan lines are transmitted to one scan lineof the LCD panel respectively. Here, P+Q<L, and P, Q, L are naturalnumbers. Then, the odd field and the even field are displayed on the LCDpanel. It should be noted that the labels bracketed by dotted linesrepresent the horizontal scan lines with respect to the labels do notuse line pairs and (*2) represents the condition that there are two lesslines after using the line pair method. It means that the horizontalscan lines with respect to the labels are not displayed.

For example, the odd field of Z in FIG. 5 includes the horizontal scanlines {1, 2, 2, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 10, 10, . . . }. It showsthat the horizontal scan lines {2, 4, 5, 6, 7, 8, 10, 11, . . . } of thehorizontal scan lines {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, . . . }included in one frame of the original TV signal are transmitted to twoconsecutive scan lines of the LCD panel respectively. The firsthorizontal scan line is transmitted to one scan line of the LCD panelwhile the horizontal scan lines {3, 9, 15, 21, . . . } are nottransmitted. Similarly, the even field of Z in FIG. 5 includes thehorizontal scan lines {1, 1, 2, 2, 3, 3, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9,11, 11, . . . }. It shows that the horizontal scan lines {1, 2, 3, 5, 6,7, 8, 9, 11, 12, . . . } of the horizontal scan lines {1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, . . . } included in one frame of the original TVsignal are transmitted to two consecutive scan lines of the LCD panel.The horizontal scan lines {4, 10, 16, 22, . . . } are transmitted to onescan line of the LCD panel.

In the driving method described in FIGS. 4 and 5, which horizontal scanline is transmitted to two consecutive scan lines of the LCD panel;which horizontal scan line is transmitted to one scan line of the LCDpanel; and which horizontal scan line is not transmitted; can be decidedin many ways as long as the following conditions are met. The conditionsinclude: the h^(th) horizontal scan line of the odd field is transmittedto the g^(th) scan line of the LCD panel when the odd field isdisplayed, and one of the (h−1)^(th), the h^(th) and the (h+1)^(th)horizontal scan lines is transmitted to the g^(th) scan line of the LCDpanel when the even field is displayed, wherein h and g are naturalnumbers with h≦L and g≦M.

It should be noted that each horizontal scan line is shown on at least ascan line of the LCD panel in the driving method described in FIG. 4.However, a portion of the horizontal scan lines is not shown on the LCDpanel in the driving method described in FIG. 5. Hence, the resolutionof the driving method described in FIG. 5 is lower than the onedescribed in FIG. 4.

In summary, the driving method for the LCD panel according to thepresent invention utilizes the line pair driving method to transmit thehorizontal scan lines of a frame to the LCD panel and the columninversion driving method to display the frame on the LCD panel. Hence,the resolution of the frame can be increased without the need to provideadditional memories or use sophisticated algorithms.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A driving method for a liquid crystal display (LCD) panel fordisplaying a frame having a first field and a second field on the LCDpanel such that each of the first field and the second field includes Lhorizontal scan lines, wherein the LCD panel includes M scan lines and Ndata lines, the driving method comprising: sequentially receiving thehorizontal scan lines of the first field and transmitting the horizontalscan lines of the first field to the LCD panel for displaying the firstfield; wherein P of the horizontal scan lines of the first field aretransmitted to two consecutive scan lines of the LCD panel respectively,and Q of the horizontal scan lines are transmitted to one scan line ofthe LCD panel respectively; and furthermore, the order of any two of thehorizontal scan lines transmitted to the LCD panel is identical to theorder of any two of the horizontal scan lines of the first field; andmoreover, the signal polarity of odd-numbered data lines of the datalines and the signal polarity of even-numbered data lines of the datalines of the LCD panel are a first polarity and a second polarityrespectively; and sequentially receiving the horizontal scan lines ofthe second field and transmitting the horizontal scan lines of thesecond field to the LCD panel for displaying the second field; wherein Rof the horizontal scan lines of the second field are transmitted to twoconsecutive scan lines of the LCD panel respectively, and S of thehorizontal scan lines are transmitted to one scan line of the LCD panelrespectively; and furthermore, the order of any two of the horizontalscan lines transmitted to the LCD panel is identical to the order of anytwo of the horizontal scan lines of the second field; and moreover, thesignal polarity of the odd-numbered data lines of the data lines and thesignal polarity of the even-numbered data lines of the data lines of theLCD panel are the second polarity and the first polarity respectively;wherein the first polarity and the second polarity are oppositepolarity; L, M, N, P and R are natural numbers; Q and S are non-negativeintegers; P+Q≦L; and R+S≦L.
 2. The driving method for the LCD panel ofclaim 1, wherein P+Q=L, and R+S=L.
 3. The driving method for the LCDpanel of claim 2, wherein P=M−L, and Q=2L−M.
 4. The driving method forthe LCD panel of claim 2, wherein Q≠0 and S≠0; the h^(th) horizontalscan line of the first field is transmitted to the g^(th) scan line ofthe LCD panel; and one of the (h−1)^(th), the h^(th) and the (h+1)^(th)horizontal scan lines of the second field is transmitted to the g^(th)scan line of the LCD panel; wherein h and g are natural numbers, h≦L andg≦M.
 5. The driving method for the LCD panel of claim 1, wherein thefirst polarity has a positive value and the second polarity has anegative value.
 6. The driving method for the LCD panel of claim 1,wherein the first polarity has a negative value and the second polarityhas a positive value.
 7. The driving method for the LCD panel of claim1, wherein P+Q<L, and R+S<L.
 8. The driving method for the LCD panel ofclaim 7, wherein Q≠0 and S≠0; the h^(th) horizontal scan line of thefirst field is transmitted to the g^(th) scan line of the LCD panel; andone of the (h−2)^(th), the (h−1)^(th) and the h^(th) horizontal scanlines of the second field is transmitted to the g^(th) scan line of theLCD panel; wherein h and g are natural numbers, h≦L and g≦M.